1. Technical Field
The present invention relates to a nanogel electrolyte for dye-sensitive solar cells including nanoparticles, and more particularly, to a nanoparticle containing an imidazolium salt chemically bonded thereto, a method of preparing the same, and a nanogel electrolyte for dye-sensitive solar cells including the same.
2. Description of the Related Art
Recently, the development of next generation clean energy has become a major issue due to severe environmental pollution and depletion of fossil fuels. Particularly, it is expected that a solar cell, that is, a device capable of converting sunlight directly into electrical energy, will become an energy source capable of solving future energy problems as they generate little air pollution, their resources are inexhaustible and they have semi-permanent life. Such solar cells are broadly classified into three main types, i.e., inorganic solar cells, dye-sensitive solar cells and organic solar cells, depending on the materials used. In inorganic solar cells, single crystal silicon is mainly used. Such singe crystal silicon solar cells have a merit of being fabricated as thin film type solar cells. However, there are problems in that they are too expensive and have low stability.
A dye-sensitive solar cell developed by Gratzel et al. (Switzerland) in 1991 is a photoelectrochemical solar cell based on an oxide semiconductor electrode comprising nanocrystalline titanium oxide particles, which transport both photosensitive dye molecules capable of generating electron-hole pairs by absorbing visible light and the generated electrons. This dye-sensitive solar cell is also called a “wet etched solar cell”. This solar cell provides various merits such as a simple manufacturing process, low manufacturing costs, and practical photoelectric conversion efficiency above silicon solar cells, thereby promoting many studies on the development of such a solar cell.
Generally, the dye-sensitive solar cell has a problem with low stability of cell to modules clue to use of a liquid electrolyte. Particularly, the liquid electrolyte has difficulty in sealing and is likely to be volatilized and leaked upon increase in external temperature, thereby causing lack of electrochemical stability over a long period of time.
To solve these problems, inorganic solid electrolytes and polymer solid electrolytes have been developed in recent years. However, the use of such solid electrolytes results in poor transfer properties at an interface between electrons and ions, thereby causing noticeable decrease in photoelectric conversion efficiency, as compared with the liquid electrolyte. Further, in order to improve photoelectric conversion efficiency of non-liquid electrolytes, intensive studies have been carried out to develop dye-sensitive solar cells in a “quasi-solid state” or a “solid-state” by preparing a gel electrolyte using ionic liquids. As reported in “Journal of Fluorine Chemistry Volume 125 (August 2004), pp. 1241-1245”, a gel electrolyte is prepared by mixing a nano silica material and a liquid electrolyte. This gel electrolyte prepared by mixing the nano silica material and the liquid electrolyte has low affinity between the nano silica and the liquid electrolyte, causing the liquid electrolyte to be easily volatized at high temperatures. Further, the gel electrolyte still contains a solvent, which entails a limit in enhancement of long term stability.
The inventors of the present invention have intensively investigated to solve the aforementioned problems and found that the use of a nanogel electrolyte prepared by mixing an ionic liquid electrolyte and a nanoparticle containing an imidazolium salt chemically bound thereto can improve both long term stability and photoelectric conversion efficiency of a dye-sensitive solar cell.